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Tachometer doesn't work

Jack_K

New Member
I have a tachometer from a Chevy El Camino or Monte Carlo. When power is applied the needle spins and stops at the 6 o'clock position and will never move.
I'll attach the schematic and explain what I have done so far. I'll also attach the data sheet on the IC.
1. I measured the resistance of both meter coils at 200 ohms each (to common)
2. I replaced the LM1819 with no change in operation
3. I measured all the resistors and diodes
4. Using a signal generator connected to the 'coil' input I see pulses on pin 9, R8-9, and to the top of the .0068 cap. Nothing on pin 5, 6,or 8.
5. I replaced the .0068 cap with no change noted
6. 8.5 volts on pin 11, 13.8 volts on pin 13, and 5.1 volts on pin 1.
7. I forget which, but one coil of the tach meter has 0.0 volts and the other has 10 volts. Common has 5.1 volts.
8. The 1N4007 on the 13.8 volt input gets hot, so does the 20 ohm resistor. I'm guessing tach meter is probably bad?
 

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erquillo

New Member
hi, i have the same problem on a chevy S10, I believe is the IC LM1819 but it is hard to find in Spain or Europe.. How did you fix it?
 

erquillo

New Member
i didn' t remove it , my tachometer is goin full scale when starting motor . I supposed it by IC fault . is on Chevy S10 sport 1989 4.3i 6 cylinder. but the tachometer scale metal plate is marked 4CYL/DSL and it's confuse me . I found the chip LM1819 or CS289gn14 like equivalent in China . is very hard to find second hand parts for this car in Europe. I checked de diodes and resistors and it is fine .
I change the distributor assembly , but I don't believe about the controller chip that generate pulses for coil for sparks because the signal is from there.
thanks
 

shortbus=

Well-Known Member
Most Helpful Member
but the tachometer scale metal plate is marked 4CYL/DSL
Not sure but think diesel engines use a different type of tach. An ignition engine gets the tach signal from the ignition module, but a diesel engine doesn't have a spark ignition.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Not sure but think diesel engines use a different type of tach. An ignition engine gets the tach signal from the ignition module, but a diesel engine doesn't have a spark ignition.
Yes, no spark plugs - so they probably generate pulses elsewhere, and choose to do it as four cylinder, as the number of cylinders makes no difference.
 

erquillo

New Member
isually at least in Europe , the diesel engines use a sensor on the fly wheels or a hall effect sensor with a system like ignition module . I collect this car abandoned into a friend's farm that he used 6 months but I don't know the history , only know it was imported used from USA to other country neither Spain , may be UK , I found parking ticket hidden , it got Spain at 97 so I don't know how many hand does it on it . I found Metric screws inserted instead inch Screws , air filter oversized and under pressure ... and so on...
the tacho full scale is 5.500 rpm but is written " unleaded fuel only "
 

shortbus=

Well-Known Member
Most Helpful Member
choose to do it as four cylinder, as the number of cylinders makes no difference.
Don't know about that, but since the S-10 diesel was a 4 cylinder I think that's why the tach face says that. But do know the pulses for the tach in a US built GM are half of the cylinder count, 2 for a 4cyl, 3 for a 6cyl and 4 for a 8cyl.

Since the TS tach say's diesel and it has a 4.3 V6 in it now, either the motor is a replacement or the tach is.:)
 

picbits

Well-Known Member
On a lot of older cars, the tacho speed was taken from the alternator and was typically 5-7 times the frequency you'd expect from a points based system.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Don't know about that, but since the S-10 diesel was a 4 cylinder I think that's why the tach face says that. But do know the pulses for the tach in a US built GM are half of the cylinder count, 2 for a 4cyl, 3 for a 6cyl and 4 for a 8cyl.
Are those petrol or diesel?, the only reason for different cylinder counts is when it's ignition based, otherwise there's no need - if it's based simply on engine rotation (as you would expect with a diesel) it's just an arbitrary design choice. But for a petrol engine, the ignition system makes an obvious (and already present) source for tacho signals, and obviously dependent on the number of cylinders, but also on the number of ignition coils (presumably a 6 cylinder dual coil system would only provide 3 cylinder pulses?).
 

shortbus=

Well-Known Member
Most Helpful Member
Are those petrol or diesel?, the only reason for different cylinder counts is when it's ignition based, otherwise there's no need - if it's based simply on engine rotation (as you would expect with a diesel) it's just an arbitrary design choice. But for a petrol engine, the ignition system makes an obvious (and already present) source for tacho signals, and obviously dependent on the number of cylinders, but also on the number of ignition coils (presumably a 6 cylinder dual coil system would only provide 3 cylinder pulses?).
They are petrol engine based. And the signals are based on the older HEI single coil ignition. Which his 4.3 should have.

Many/most diesel engines use the alternator as a signal source for the tach.Unless it is an older shaft drive tach.


 

wkrug

Active Member
When Pulses are visable at Pin 9 than at Pin 6 must be shown pulses too.
Much smaller, but visible.
Probably there is a short ( Whisker ?! ) between any copper lines on the PCB?
The only connection +B of the 1N4007 Diode is to overvoltage Protection ( 1N4746 ) and the Voltage Divider ( 470Ohms / 1N4733 ).
When all that parts are OK the LN1819 is the only Part in this Line - But that was replaced.
How much Current the Instrument draws from the +B Line?
When soldered out the LN1819 how much then?
And where this current goes?
 

erquillo

New Member
Hi again.
i solve the problem , I don't know why one resistor was missing , maybe it is embebed into a white IC with several resistors inside . the resistor connected between the pin 5 and 8 on LM1819. I changed the LM1819 and the tacho doesn't work. the same problem , very hight gain so when starting at 1000rpm goes to full scale . that resistor controls the gain , it means angle of deflection . I installed 1M adjustable and make calibration , 0 and full scale patiently . because I move the needle from air core meter and the 0 calibration was lost. for calibration made a circuit NE555 simulator pulse , checked with oscilloscope measuring time of waveform .
 

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